Man's physical universe

356 FORMS OF ENERGY of

356 FORMS OF ENERGY of aircraft, the skill of mechanics, the accuracy of navigators, and the service of meteorologists. There Is a Definite Lag between Fundamental Research and Its Practical AppUcation. The aerodynamic advantages of an unbraced monoplane were recognized in the days of braced biplanes, but it required the invention of light aluminum alloys of great strength and improved techniques in wood construction to make monoplanes practical. Fig. 149. SBD Douglas dive-bomber. A low-wing type. Douglas Aircraft Company.) (Courtesy of the The advantages of retractable landing gears and wheels were pointed out long before they were actually used in airplanes because they became economically practical only when high-speed planes made them increasingly desirable and thick cantilever wings made them possible. There Are Four Types of Monoplanes. The four types of monoplanes differ in the point where the wings are attached to the body (fuselage). In the parasol type, the wings are above the fuselage. The high-wing type of monoplane has its wings at the top of the fuselage.

AIRPLANE A TRIUMPH OF MODERN SCIENCE 357 The mid-wing type of monoplane is uncommon, and the low-wing type of monoplane is best adapted to military service and commercial use where upward vision is an important factor. Biplanes offer some advantages in maneuverability, but their external bracing offers too much drag for high speeds. There are certain definite reasons for each type of airplane design such as speed, high rate of climb, stability, maneuverability, range, and capacity. Rotary-wing Airplanes Make Possible a Direct Take-off. The autogiro and the helicopter are typical examples of rotary-wing airplanes. An interesting feature of some autogiros is that the blades may be folded back over the horizontal tail surfaces of the machine while on the ground, thus permitting the machine to be driven down a highway and also reducing the hangar space required. The helicopter can go forward, backward, or sidewise. It can stand still in the air. It can land so gently that the wheels will not move more than a very short distance after touching the ground. The helicopter differs from the autogiro in that it has no regular propeller but depends upon tilting the rotor for forward or backward motion. The modern autogiro has a rotating wing; it depends upon its whirling blades to keep it in the air; these blades operate even when the engine fails, to permit a safe landing. The autogiro has a propeller which gives it a forward speed of 125 miles per hour. One future application of rotary-wing airplanes, for which they are well adapted, is the ferrying of passengers from airports in the outskirts of metropolitan centers to landing areas on roofs in the centers of business districts. Occasionally more time is consumed in traveling the few miles to and from airports in cities than in traveling by airplane between airports hundreds of miles apart. Fig. 150. The autogiro. (Courtesy of Science Service.)